The invention generally relates to photovoltaic devices. More particularly, the invention relates to improved interfaces for photovoltaic devices.
Thin film solar cells or photovoltaic devices typically include a plurality of semiconductor layers disposed on a transparent substrate, wherein one layer serves as a window layer and a second layer serves as an absorber layer. The window layer allows the penetration of solar radiation to the absorber layer, where the optical energy is converted to usable electrical energy. Cadmium telluride/cadmium sulfide (CdTe/CdS) heterojunction-based photovoltaic cells are one such example of thin film solar cells.
Cadmium telluride (CdTe)-based photovoltaic devices typically demonstrate relatively low power conversion efficiencies, which may be attributed to a relatively low open circuit voltage (Voc) in relation to the band gap of the material which is due, in part, to the low effective carrier concentration and short minority carrier lifetime in CdTe. There is also an increased drive for decreasing the thickness of the CdTe layer because of the low availability of tellurium and also increased interest in photovoltaic devices with “n-i-p” configuration. However, current CdTe devices may have significant recombination of electron-hole pairs at the front interface between CdS and CdTe. Furthermore, thinner CdTe may also lead to recombination of electron hole-hole pairs at the back contact of the CdTe photovoltaic device. Recombination of electron-hole pairs may lead to lower open circuit voltage and thus lower efficiencies.
Thus, minimizing the recombination of the electron/hole pairs at one or both the front interface and the back interface in thin film CdTe photovoltaic cells may be desirable. Thus, there is a need to provide improved photovoltaic device configurations having desired short circuit current (JSC), open circuit voltage values (VOC), fill factor (FF), and efficiency values.